Bifocal lens blank



Nov. 2, 1943. G. A. CLEMENT i 2,333,362

I BIFOCAL LENS BLANK Filed April 1, 1942 lNVE TOR 620265 A. Effi/vz' ATTORNEY Patented Nov. 2, 1943 UNITED STATES PATENT OFFICE `BIFOCAL LENS BLANK George A. Clement, Mount Vernon, N. Y.

Application April 1, 1942, Serial No. 437,135

2 Claims.

This invention has particular reference to the -marking of bifocal lens blanks to denote their individual additions. The powers ofbifoca1 lenses are usually prescribed on the basis 4of the correction for distance; that is, the dioptric power of the distance lens portion is given and the power of the reading or near field is figured by determining the amount that has to be added to the power of the distance field, and that amount is given in the prescription and is known as the addition or added power.

The added power of a bito-cal lens blank is predetermined and the transforming of the blank into a iinished lens does not aiiect the added power. A given blank may perhaps be susceptible of selectively producing any one of several inished lenses, each one with a different power for distance vision, but the near power will be stronger than the distance power by the predetermined added power, irrespective of the prescription selected.

To enable the workman to identify the blanks and determine readily the one to choose for a given prescription, it is customary to mark the addition on the edge of every blank. This has usually been done by scratching the figures in the edge of the glass blank, for example 2.25, meaning two and one-quarter diopters addition.

The diiculty of writing in glass in this manner is manifest, with the result that frequently the writing is not legible. But a still greater shortcoming in this manner of marking arises from the fact that the successive steps in transforming the blank to a finished lens reduces the thickness of the blank and thus grinds off the top and bottom portions of the figures, oftentimes destroying their legibility.

The form of marking contemplated by this invention obviates this diiiiculty. Transverse lines either in the form of grooves or of raised ribs are provided on the edge of the blank, selected in number and arrangement to denote the addition. The lines denoting the integral units of dioptric power are on the left, and spaced therefrom to the right are lines denoting fractional units of one ouarter diopter each. Two lines on the left therefore denote two diopters, and tWo lines on the right denote half a diopter.

Grinding down the blank merely shortens theA lines but they remain easily and unmistakably discernible down to the condition of the iinished lens ready for edging.

The embodiment chosen for illustration in the accompanying drawing will now be described.

r fused in the countersink.

Fig. 1 is a perspective of a rough blank einbodying the invention.

Fig. 2 is an edge view of the same.

Fig.r 3 is a View similar to Fig. 1 showing the blank in semi-finished Condition.

Fig. 4 is an edge View of thesarne.

Fig. 5 is an edge View of the finished lens ready for edging.

Figs. 6 to 13, inclusive, are edge vieWs of a set of eight blanks having the characteristic marking and comprising an example of all the blanks within a selected range of added powers, in this case from one diopter to 2.75 diopters.

The form of blank selected for illustration is of the fused bifocal type, but the invention is adaptable with other forms of bifocal blanks.

In the fused bifocal art the major blank of glass of lower index of refraction is molded usually intomeniscus or flat form, and a countersink of predetermined curvature is ground and finished in one face, and a Piece of glass of higher index of refraction, commonly termed the segment or button, is iinished on one side and is fused into the countersink. The fused blank is either sold in that rough form, or is ground and finished in the factory to a selected base curve on the bifocal side, leaving to the one who lls the prescription the job of grinding and finishing the other` side to the form which will satisfy the prescription.

Turning now to the drawing, Figs. 1 and 2 show the rough fused blank. The major blank l0 of meniscus form has a countersink Il ground and polished in its upper face and a button l2 is In the edge are the identifying grooves in two spaced groups, the grooves I3a on the left denoting the units of dioptric power of addition, and the grooves I 3b on the right denoting the fractions of dioptric power of addition. In this case, since there are two of each. the added power is 2.50 diopters.

In Figs. 3 and 4 the blank is shown in a further stage of treatment. It has been ground and iinished on its bifocal side. As seen this somewhat reduces the thickness of the blank, but the lines Ia and lsb are nevertheless easily discernible.

In Fig. 5 the blank is shown reduced to a iinished lens ready for edging. This is done by grinding and polishing the opposite side to suit the prescription. This final treatment leaves the glass lens so thin that any writing on the lens would be practically obliterated. However the grooves are still unmistakable and may be easily detected with the thumb nail.

The produci-l consisting of a complete set is edge with a proper grinding tool, inrwhich case 10 the letter X might be used to denote that the whole units are zero. Also of course the lines may be molded in the edge in which case theymay be raised, if desired. However sinethelwn major blanks from a given mold may result in15 fused blanks of various powers ofaddition, it ispreferable t0 mark the blanks' after their addi tion has been determined. It is obvious that the invention is equally applicable to one-piece bifocal blanks, and that 20 other modificationsl will suggest themselves l to those skilled in the art, within the scope ofthe appended claims.-

I claim: y

1. A product in lthe manufacture of 1bifocal lenses comprising a set of ,bifocal lensrblanks progressing from lowest to highest addition and having appreciable transverse lines indicative of the respective dioptric powers of addition formed upon their edges, there being one line for each integral unit of added dioptric power and one line for each fractional unit of added dioptric power, the lines of each denomination being grouped in immediate juxtaposition and the two groups being appreciably spaced.

A 2. A product in the manufacture-i of bifocal lenses comprising a set of bifocal lens blanks progressing from lowest to highest addition and j each formed by fusing a small piece of glass of relatively vhigh index of refraction into a countersink inv one face of a major piece of glass of lower t index of refraction, the blanks having transverse grooves in their edges forming lines indicative of their respective dioptric powers of addition, there being one line for each integral unit of added dioptric power and one linefor each` fractional unit of added dioptric power, therlines of each denomination being grouped in` immediate juxtaposition and the two groups being appreciably spaced. 1

Y GEORGE A. CLEMENT.` 

